Holographic patterning method and tool for production environments

ABSTRACT

A high resolution, high-throughout, large field size, production environment, lithographic tool system and method includes an interferometric pattern generator utilizing three or four mutually coherent optical beams organized in a flexible beam expansion, filtering, aperturing, and delivery system, large area pattern uniformity is attained via optimized illumination beam positioning and shaping. A passive stabilization system achieves fully modulated interferometric patterns in high mechanical and acoustical vibration manufacturing environments.

This is a continuation of U.S. provisional application Ser. No.60/019,491, filed Jun. 10, 1996.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and apparatus for highthroughput holographic microlithography in which interferometricpatterning techniques suitable for producing periodic arrays ofsub-micron sized structures are adapted for and incorporated into ahigh-throughput, large field size manufacturing tool. The method andtool of the present invention have applications in the display,semiconductor, and optics manufacturing industries.

2. Description of the Prior Art

An unmet need exists for an efficient tool adapted for production offlat panel displays based on distributed cathode field emission display(FED) technology, a strong competitor in the flat panel display marketcurrently dominated by liquid crystal display (LCD) manufacturers. A FEDis a distributed cathode, flat panel analog to the well known cathoderay tube (CRT). Essentially, billions of miniature electron `gun`cathodes are distributed spatially over the surface of a displaysubstrate. Electrons are emitted from the tiny cone-shaped cathodesunder the influence of a high accelerating potential, and strike aphosphor screen placed over a common anode and are thereby converted tophotons (i.e., light). The most critical step in the fabrication of theFED distributed cathode matrix is patterning of an array of holes orwells in which emitter cones are grown. In the prior art, aphotosensitive medium such as photoresist has been employed to record animage of a hole array formed by conventional photo- lithographictechniques such as shadow masking (contact printing), opticalprojection, electron or laser beam direct writing. The hole array orpattern, in photoresist, can then be used as an etch mask in the processof forming the holes. In the prior art, hole patterns have been limitedby resolution and field size of the imaging or writing systems, andcomplex, often expensive, work-around solutions have been required toachieve modest field sizes of fifty by fifty mm with hole diameters inthe one to two micron range. Recent research has demonstrated thatreduction in the hole size (and consequently the emitter size), belowthe one micron range provides numerous benefits such as a reduced gatevoltage, lower power consumption, greater current densities per pixel,and built-in redundancy. Thus, to fully realize the potential of FEDtechnology, an inexpensive, high speed, production environmentlithographic tool, incorporating a patterning technology capable ofproducing large-area, high-density, sub-micron diameter hole arrays withfew defects and at low cost, is needed.

Holographic or interferometric lithography has been proven in laboratoryenvironments to be feasible for generating the high-resolution periodicstructures suitable for flat panel FEDs and exploits the mutualcoherence of multiple optical beams derived from a single light sourcesuch as a laser. The laser beams are made to overlap in some region ofspace and interfere to produce patterns of light and dark areas thatrepeat on a scale proportional to the wavelength and are subsequentlyrecorded in photosensitive media such as photoresist. Conventionalcontact or projection photo masks are not required and so holographiclithography is known as a "maskless" lithography technique. In addition,by exploiting inherent photoresist and etching process non-linearities,a variety of surface relief structures can be generated with no changein the optical configuration.

Other useful surface relief structures can be patterned usingholographic lithography such as a "motheye" or sub-wavelength-structure(SWS) surfaces. Motheye surface structures have been shown to beeffective for nearly eliminating the reflectance of light from anoptical interface such as between air and a window or a refractiveoptical element. The term "motheye" is derived from the insect's eye, anatural analog; it was observed that the eye of a nocturnal insect(e.g., a moth) reflected little or no light regardless of the lightwavelength or the angle at which incident light struck the eye surface.The eye surface functions in a manner similar to a graded indexmaterial, essentially allowing the smooth transition between media withdiffering bulk density. To avoid diffraction effects, synthetic motheyesurfaces must be fabricated with feature sizes and spacings smaller thanthe wavelength of light incident upon the surface. For most infrared orvisible wavelength applications, this necessitates structure spacings inthe sub-micron to sub-half micron range, patterned over the entiresurface (e.g., window or optic area). A means for manufacturing motheyestructures in high volumes and over large areas is not available in theprior art and a variety of products could benefit from the increasedruggedness and anti-reflective performance afforded by motheye surfacingover large areas.

Manufacture of liquid crystal displays (LCDs), also requiresimprovement. Liquid crystals (LCs) are anisotropic molecules which canaffect the properties of light with which they interact, and, under theinfluence of an electric field, can vary the magnitude of this affect.LCDs are formed by the creation of a cell, typically constructed usingglass, within which the LC molecules are confined. The term "crystal"refers to the structure or ordering of the LC molecules into a definableor measurable state typically found with molecules in a solid state.This artificially created ordering is accomplished by depositing thinlayers of material on the boundaries of the cell, which eitherphysically, or electrostatically force the LC molecules topreferentially align in one direction. The "alignment layers" as theyare known in the art, are typically processed using a physical rubbingor buffing technique comprising a spinning drum or cylinder and rollingit over the cell substrate coated with alignment material. High levelsof hazardous static charge and spreading particulate (from the rubbingmaterial) are generated during this process; in addition, manufacturingyields can be improved.

SUMMARY OF THE INVENTION

LCD manufacturing yield increases are provided by incorporating anon-mechanical, non-contact alignment layer process which avoidsproblems with static charge and is compatible with existingmanufacturing equipment and environments. The process of the presentinvention includes patterning surface structures into an alignmentmaterial layer. Using the holographic lithography techniques of thepresent invention, surface structure LC alignment layers are producedwith the enhanced anti-reflective properties of motheye surfaces. Byproducing sufficient asymmetry in the surface structures, the patterningprocess allows control of both angular rotation and angular tilt (knownas pre-tilt or tilt-bias in the art) of the LC molecules with respect tothe cell walls.

It is, therefore, an object of this invention to provide a holographiclithography patterning tool enabling the high-volume processing of LCstructures.

It is also an object of this invention to provide a holographiclithography patterning tool enabling the high-volume manufacturing oflarge-screen area flat panel displays based on FED technology.

It is another object of this invention to provide a manufacturing toolcapable of producing motheye antireflection surface relief patterns forvisible and infrared window and optics applications, and for the diamondfilm industry. As noted above, the LCD industry can also benefit fromthis invention which allows the production of structured alignmentlayers with enhanced optical performance and greater product yield. Verylarge scale integration (VLSI) semiconductor and electro-optic devicemanufacturing can also use the method and tool of the present inventionin sub-half micron processes and optical beam modulation devices.

These and other objects of the invention are attained by providing amanufacturing tool having four major components: first, a source ofpolarized, coherent optical radiation with a wavelength suitable forexposing photosensitive media such as that derived from a laser; second,a flexible, re-configurable beam delivery system with a means to divideand re-direct, or fanout the coherent radiation into a two, three orfour beam interferometric configuration; third, a structure for dampingthe acoustical and mechanical vibrations typical of manufacturingenvironments; and fourth, a mechanized two-dimensional translationstage, panel or wafer mount with a computer controller for replicatingthe patterning area over arbitrarily large substrates.

Holographical lithography demonstrations in the laboratory have employedUV wavelength light derived from an argon ion gas laser which is highlyautomated and reliable, making it a good choice for a manufacturingtool. A wavelength in the deep blue spectral range is also availablewith argon ion gas lasers; the wavelength choice becomes a tradeoffbetween photoresist sensitivity and laser power. A large variety ofphotoresists possess high sensitivity to energy in the near UV spectralrange, whereas the number of photoresists sensitive to energy having avisible blue wavelength is more limited, and in those photoresists,sensitivity is typically lower. However, the blue wavelength iscurrently the more practical choice for a manufacturing tool, for anumber of reasons: first, the divergence of an optical beam for a givenwaist or aperture size decreases for shorter wavelengths (a relationshiphaving a direct impact on field size in the proposed system--field sizeis 30% larger for 458 nm light than for 351 nm--again given a fixedaperture size); second, alignment and maintenance of a holographic setupis greatly simplified when operating with a visible, relatively eye-safelight source; and third, laser lifetime for the argon-ion gas laser isdramatically reduced when operated at near UV wavelengths. A productionenvironment laser, consequently, is expected to last up to two timeslonger when operated at 458 nm. Finally, a flexible beam delivery systemis an integral component of the present invention and requiresspecialized optical fibers which, to date, exhibit inferior, unstable,and impractical performance when guiding UV wavelength light.

Laboratory demonstrations have produced two-dimensional patternsutilizing two-beam holographic technology but requiring cumbersomemechanical rotation between two superimposed recordings, and so are notpractical in a production tool system. Consequently, a further object ofthis invention is to provide a patterning system based on three or fourbeam interference, requiring only a single exposure to generatetwo-dimensional arrays of holes, cones, posts, tips, vias, mesas, grids,or micro lenses. Multi-beam intensity patterns also inherently possess agreater contrast between light and dark areas, yielding structureshaving higher aspect ratios.

Another significant object of this invention is to replace theconventional, mechanically unstable spatial filters of the prior artwith single mode, polarization maintaining optical fibers, therebyeliminating optical noise and providing highly divergent, large areabeams and providing a flexible means for controlling and modifying theoptical configuration. In addition, the flexibility afforded by opticalfibers allows equalization of beam path lengths and elimination of thelongitudinal mode suppressing etalon incorporated in the gas lasersource. This improvement results in a gain in laser power (by nearly afactor of two) and consequently a doubling of throughput.

Equalization of optical beam path lengths is also facilitated byemploying a non-conventional means for dividing the multiple beams intoequal parts. A single diffracting element such as a binary-phase Dammanngrating (or a more efficient arbitrary-phase fanout) is employed toyield multiple equal intensity beams with negligible path lengthdifferences attributable to the dividing process. Diffractive elementscan also be integrated with passive or active waveguides to yield ahighly flexible and compact system for controlling the relative phasebetween each of the output beams.

A further object of this invention is to provide a means for generatingvery large. area patterns, greater than that afforded by the naturaldivergence of an optical beam exiting an optical fiber. A field sizeenlargement technique is disclosed and is based on the combination ofoptical fibers with diffusing (or random scattering) optical elements.Diffusers are employed by those skilled in the art of producingholograms of real world objects. Diffusers disrupt the spatial coherenceof the illuminating beam, thereby reducing the local interference noisecaused by light reflected from various object features. Diffusers alsoproduce a level of spatial optical noise due to their scatteringfunction, an unacceptable result when recording interference patterns.In the prior art, researchers have worked around this problem bymechanically rotating the diffuser to average out spatial noise overrecording time, a solution impractial in a production environment, dueto the resulting loss in patternable volume creating an imaging-likeproblem similar to poor depth of focus. An aspect of the presentinvention is the discovery that when highly divergent light from anoptical fiber is directed through a diffuser, the level of spatial noise(or speckle) introduced by the diffuser is vastly reduced, while thefunction of beam enlargement is maintained, and beam divergence isincreased by a factor of two or more with only a slight increase in thelevel of spatial noise. Specially adapted diffusers can be producedwhich further enhance the illumination uniformity by varying the radialscattering rate and thereby producing illuminating beams with littlevariation in intensity. The advantageous combination of a fiber opticwaveguide and a diffuser aberrates the resulting illumination, thusaveraging out the spatial noise and reducing errors in the resultingholographic pattern.

A final object of this invention is incorporation of an improvedillumination setup in a manufacturing tool, yielding more uniformfeature size patterning over larger areas. The enhanced feature sizeuniformity is attained using two techniques. First, the phase of eachbeam is aberrated to reduce feature distortions and feature spacingvariations resulting from the enlarged beams. Second, illuminationuniformity is enhanced by overlapping the centroids of the illuminatingbeams in a plane located a fixed distance from the recording plane. Fora given field size, the fixed distance is optimized together with thebeam divergence to produce no more than 15% variation in the intensityof integrated illumination. Photoresist modelling shows that variationyields a maximum of five percent variation in recorded feature size.

The aforesaid objects are achieved individually and in combination, andit is not intended that the present invention be construed as requiringtwo or more of the objects to be combined unless expressly required bythe claims attached hereto. The above and still further objects,features and advantages of the present invention will become apparentupon consideration of the following detailed description of a specificembodiment thereof, particularly when taken in conjunction with theaccompanying drawings wherein like reference numerals in the variousfigures are utilized to designate like components.

DESCRIPTION OF THE DRAWINGS

FIG. 1a is a front elevation view in partial cross section of apatterning head of the tool system of the present invention.

FIG. 1b is a side elevation view in partial cross section of thepatterning head of FIG. 1a.

FIG. 2 is an perspective view in partial cross section of the toolsystem remote control tower and water-to-water heat exchanger.

FIG. 3 is an overhead or plan view of the laser source platform anddepicts the dividing and coupling of the free space laser beam into thefiber optic cables.

FIG. 4a is an overhead or plan view of the beam delivery breadboard withassociated rails for the three beam delivery systems.

FIG. 4b is an overhead or plan view of the beam delivery breadboard withassociated rails for the four beam delivery system.

FIG. 5 is an overhead or plan view of the recording plane translationstage and substrate mounting system, or chuck; also depicted is amaximum-size substrate with a typical pattern area.

FIG. 6a is an optical schematic diagram of the flexible beam deliverysystem based on fiber-optic cables; a four beam configuration is shown.

FIG. 6b is an optical schematic diagram of the flexible beam deliverysystem based on fiber-optic cables; a three beam configuration is shown.

FIG. 7a shows a compact 1:4 fanout structure for dividing a single lightsource into four sources.

FIG. 7b shows a compact fanout structure using three 1:2 fanouts, fordividing a single light source into four sources.

FIG. 7c depicts a grating-coupled frustrated total internal reflection(FTIR) device for dividing a single light source into multiple sources.

FIG. 7d depicts an integrated optic waveguide structure employing modecross coupling for dividing a single light source into multiple sources.

FIG. 8a is a computer generated contour plot of intensity distributionsfor a tool system not employing shifted three-beam illumination;superimposed on the plots is a rectangle representing the screen area ofa typical 300 millimeter diagonal display.

FIG. 8b is a computer generated contour plot of intensity distributionsfor a tool system including the shifted three-beam illumination of thepresent invention; superimposed on the figure is the rectanglerepresenting the screen display, as in FIG. 8a.

FIG. 9 is similar to FIG. 8b but illustrates the intensity distributionsplotted for a four-beam tool system having shorter displacement and alower beam divergence.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1a and 1b are, respectively, a front elevation view in partialcross section and a side elevation view in partial cross section,illustrating the patterning head 10 of the tool system of the presentinvention. Patterning head 10 is part of a cluster of tools making up amodern display manufacturing facility. Patterning head 10 includes threemain levels: the lowest level 12 contains a laser illumination source 14on a platform 15 (an embodiment of a laser illumination source is shownin FIG. 3); the middle level 16 is a panel mount or chuck 18 (i.e., forpanel or workpiece 19) and X-Y translation stage 20 (detailed in FIG.5); and a beam delivery breadboard 22 (e.g., as shown in FIG. 4a),mounted in a gantry support system 24 supporting first, second and thirdcarriage mounted fiber positioning stages 25a, 25b and 25c, comprisesthe top level 26. Deriving power and control signals from the remotelypositioned control tower (shown in FIG. 2), patterning head 10 providesthe production environment framework within which holographic patterngeneration requirements can be met. In particular, there is arequirement for isolating the laser beam paths 27a, 27b, 27c and therecording plane (e.g., the upper surface 28 of workpiece 19) fromvibrations due to excessive air flow, mechanical equipment vibrations,acoustic noise and any other ambient source of vibration. Vibrationisolation is provided for all three levels 12, 16 and 26 in patterninghead 10 using four vertical pneumatic passive damping supports 30.Pneumatic supports or isolators 30 float the patterning head 10 oncompressed air. To attenuate vibrations from air currents and airborneacoustic noise, both the laser source walls 31 and the patterningchamber walls 32 are enlcosed using aluminum or stainless steel skinned,foam core panels typical of modern clean room wall coverings. Patterninghead 10 is tethered (to the control tower and heat exchanger supportequipment shown in FIG. 2) by the laser umbilical and a second cablebundle containing vacuum and electrical control lines.

Patterning head 10 includes a patterning chamber 34 enclosed by fourpatterning chamber walls 32 and a chamber lid 36. Patterning chamber 34can be sealed and, when sealed, is optically enclosed or light tight.Mutually coherent laser beams shine downwardly from the fiberpositioning stages 25a, 25b, and 25c, along the laser beam paths 27a,27b, 27c, and are aimed toward panel mount 18 which acts as a platformto support a workpiece to be subjected to the holographic lithographyprocess of the present invention. An aiming point 38 on the panel uppersurface 28 is approximately at the center of the laser beam paths 27a,27b, 27c.

FIG. 2 illustrates support equipment included in the tool system for usewith patterning head 10. Patterning head 10 (FIGS. 1a, 1b) is controlledusing a control tower 40 including a personal computer 48 thatinterfaces with the driving electronics, directs the patterningsequence, and monitors the tool system status. The laser source 14(FIGS. 1a, 1b) is temperature controlled via a stand-alonewater-to-water heat exchanger 44. A conventional electric air compressor(not shown) provides the requisite compressed air for the pneumatictable isolation supports 30 (FIGS. 1a, 1b). Control tower 40 alsoincludes an exposure energy meter 46 for measuring and indicating theholographic exposure energy, shutter drivers (and control relays) forcontrolling timing of the panel exposure and a stepper motor controller50 for controlling the electric stepper motors used to position the X-Ytranslation stage 20 (FIGS. 1a, 1b) upon which the panel mount 18 restswithin the patterning chamber 34. Control tower 40 is also used to housepower supply 52 for laser illumination source 14.

FIG. 3 is an overhead plan view of the platform containing an embodimentof a laser source 14' and represents an optical diagram, drawnapproximately to scale, showing the free-space laser beam path,conventional beam splitting and directing optics, fiber-optic couplingconnectors, cables and the optomechanical hardware for mounting andaligning the optics and fiber-optic cables. The laser depicted is anargon-ion gas laser 60 generating a polarized, single-frequency (oroptionally a single-line) beam with a wavelength of 457.9 nanometers, inthe blue range of the visible spectrum. As noted above, the choice ofthis wavelength contributes to the large field-size, flexible beamdelivery, and enhanced illumination uniformity advantages of the toolsystem of the present invention. Laser source 60 generates a coherentlight source beam directed through a sequence of first and secondturning mirrors 62, 64, and then to a set of one, two or three beamsplitters dividing the single beam into two, three or four equalportions, respectively. As noted above, the patterning tool of thepresent invention can include two, three or four laser beams. In theembodiment of the laser source 14' shown in FIG. 3, four substantiallyequal and mutually coherent laser beams are produced by use of firstsecond and third successively positioned beam splitters 66, 68 and 70.As is well known in the art, a beam splitter reflects a portion of anincident laser beam and allows the remainder to pass through; so, asshown in FIG. 3, a portion of the coherent light source beam incidentupon beam splitter 66 is reflected at an acute angle toward a firstelectronic shutter 72 (which is in an open, light transmissive state)and on through first waveplate 74 and is launched into the firstflexible fiber optic patch cord 76 via a connectorized mounted fiberpositioning stage 78. The light passed through beam splitter 66 isreceived by beam splitter 68. In similar fashion, the reflected energyfrom second beam splitter 68 is transmitted through second electronicshutter 80 (when in the open, light transmissive state), through secondwaveplate 82 and is launched into second flexible fiber optic patchcord84 via second connectorized mounted fiber positioning stage 86.Likewise, the light passed through beam splitter 68 is received at beamsplitter 70. The reflected energy from third beam splitter 70 istransmitted through third electronic shutter 90 (when in the open, lighttransmissive state), through third waveplate 92 and is launched intothird flexible fiber optic patchcord 94 via third connectorized mountedfiber positioning stage 96. Finally, light transmitted through thirdbeam splitter 70 is reflected from a third turning mirror, istransmitted through fourth electronic shutter 100 (when in the open,light transmissive state), through fourth waveplate 102 and is launchedinto fourth flexible fiber optic patchcord 104 via fourth connectorizedmounted fiber positioning stage 106.

The beam splitters 66, 68, and 70 serve to divide the coherent lightsource beam into first, second third and fourth mutually coherentoptical beams. As shown in FIGS. 7a, 7b, 7c and 7d, there are a numberof alternatives for dividing the source beam. In alternativeembodiments, the source beam is divided upon being directed through adiffractive one-to-four fanout 110 as shown in FIG. 7a, through seriallyarrayed one-to-two fanouts as shown in FIG. 7b, through a gratingcoupled frustrated total internal reflection device (FTIR) 111(comprised of a slab waveguide with spaced diffractive elements) asshown in FIG. 7c, or a mode cross-coupling integrated optic waveguidedivider 114 (including a slab waveguide with branching trees andoptional electro-optic phase modulators)as shown in FIG. 7d, to generatethe four beams desired.

The four beams are then incident upon fiber optic cables 76, 84, 94, 104(FIG. 3) fitted at the proximal end with pre-aligned, collimator-typefiber coupling connectors included in the respective mounted fiberpositioning stages 78, 86, 96, 106. Once launched into and contained bythe flexible fiber-optic patch cords the beams are easily manipulatedsimply by moving the fiber optic patch cords. The fiber optic cables 76,84, 94, 104 are directed through an access hole in the translation stagetable and then up along the gantry support posts to the beam deliverybreadboard level, as shown in FIG. 4b.

FIGS. 4a and 4b are overhead views of two embodiments of the laser beamdelivery breadboard. The three beam embodiment of FIG. 4a corresponds tothe patterning head embodiment 10 of FIGS. 1a and 1b. The four beamembodiment of FIG. 4b corresponds to the laser source embodiment 14'illustrated in FIG. 3. For both embodiments, each fiber optic cabledistal end is mounted in a two-axis mechanical gimbal, which in turn ismounted on a carriage type base. The carriages can be manually (or viaoptional automation) positioned along the length of rails; carriageposition defines the range of pattern feature size and pattern featurespacing. Graduated stops along the calibrated rail system are located atcommonly selected positions. Gantry support system 24 is illustrated inFIG. 4a and includes a planar support beam delivery breadboard 22affixed to four vertical granite columns or stanchions 134. A three beamrail system 118 is bolted to gantry support system 24 and includesfirst, second and third equal length rails 120, 122 and 124, radiallyspaced in a common plane and affixed to one another in a center railconnection hub 128 disposed near the center of the patterning chamber34. Rail graduation markings 126 are used to position the carriagemounted fiber positioning stages 25a, 25b, 25c, which are preferablypositioned at equal distances from the center rail connecting hub 128,as can be seen by use of the imaginary reference lines 130 included inFIG. 4a. Patterning chamber walls 32 can be seen in cross section, aswell as the four corner granite stanchion supports 134. The four railembodiment of the rail system is shown in FIG. 4b and includes first,second, third and fourth rails 136, 138, 140 and 142, respectively,arrayed in a common plane and radially spaced and affixed to one anotherat the center of the chamber 34' in a center rail connection hub 144;this embodiment also includes patterning chamber walls 32 and the fourcorner granite stanchion supports 134, as above. For the embodiments ofFIG. 4a or FIG. 4b, the entire breadboard (e.g., 22 of FIGS. 1a and 4a)is supported at the four corners by precision machined vertical granitestanchions 134. Laser beams emanating from the fiber-optic cable distalends are directed downwardly towards the translation stage/panel mountlevel, as discussed above.

FIG. 5 is an overhead view of the translation stage level 16 depictingthe range of travel or translation for the two-axis X-Y stage 20 and thepanel mount 18 including a vacuum chuck 150. In the embodimentillustrated, vacuum suction force for the chuck 150 is controlled inzones by computer; a variety of vacuum control schemes permitsaccommodation of a variety of panel sizes, up to a maximum of 650 by 550millimeters. Larger panels can be accepted with simple changes in thescale of the tool and chuck 150. Chuck temperature can be maintainedunder computer control. The chuck 150 incorporates a panel lift featureto facilitate the automated panel loading and unloading, and a beampower detector 152 is at the aiming point 38 (e.g., as in FIG. 1a) andintegrated below the chuck surface for automated exposure metering.

The illumination system of the present invention is schematicallyillustrated in FIG. 6a which shows a flexible, shifted four-beamillumination architecture. FIG. 6b schematically illustrates athree-beam embodiment. As discussed above, the beam from laser source 14is divided, in any of the manners described herein, and launched intofiber-optic cables at the cable proximal ends (e.g., at the mountedfiber positioning stages 78, 86, 96 and 106). Coupling of laser lightinto single-mode, polarization maintaining fiber (optical waveguide) hastraditionally been a difficult task due to the small fiber corediameters--typically in the two to four micron range. Recently, however,fiber-optic cable manufacturers have been "connectorizing" cableproducts with mechanical mounting hardware and optics, usually forcollimating the light emanating from the fiber ends. However, in thepresent invention, a typical fiber collimator is operated in a reversesense, whereby nearly collimated laser light is coupled into the fibersat the fiber proximal ends (e.g., at the mounted fiber positioningstages 78, 86, 96 and 106), whereupon the alignment tolerances forlaunching light into the fiber are greatly increased and couplingstability is vastly improved. These advantages, together with theflexible nature of the fiber cables, make fiber cables well suited foruse in the manufacturing tool of the present invention. Anothersurprising advantage obtained by employing fiber-optic cables is theability of fiber optic cables to replace the function of conventionalspatial filters used in laboratory setups. The act of coupling the laserlight into the fiber cable eliminates amplitude noise in the beams, andproduces highly divergent beams as a result of the confinement of thelight within the small diameter fiber core. The highly divergent beamsemanating from the ends of fiber cables, as shown in FIGS. 6a and 6b,have a high numerical aperture. The fibers are cut to lengths whichallow the optical path lengths to be set equal, thereby allowing thelaser to operate at an increased power level afforded by the presence ofmultiple longitudinal modes, or, using industry terminology, single-lineoperation. Connectorized on the distal end of each fiber, an opticalelement 160 (i.e., a conventional refractive lens) can be employed tooptimize the divergence of the illuminating beams illuminating theworkpiece. However, in the preferred embodiment, optical element 160 isa conventional diffusing element imparting both phase and amplitudenoise or aberration which, in conjunction with the highly divergent beamemanating from the fiber distal end, tailors the phase noise. Asdiscussed above, this combination yields precise control over theilluminating beam divergence without the unacceptable spatial noise asis typically found when using diffusers. The advantageous combination ofa fiber optic waveguide and a phase aberrating diffuser modifies theresulting illumination beam, thus averaging out the spatial noise andreducing errors in the resulting holographic pattern. Optical element160 is preferably a diffuser having a diffusing angle in the range of5°-40° (uniform or gaussian) and is preferably selected to optimizemicroscopic feature uniformity; at present a diffuser having a diffusingangle of 10° is being experimented with. Alternatively, optical element160 can be a mirror including diffusing and enlarging surfaces, employedin a reflective-mode operation. In the three-beam embodiment of FIG. 6b,the cable distal ends 164 are located in a common plane 166 and in atriangle arrangement; the recording plane 168 is located at a fixeddistance (e.g., greater than one meter) from and parallel to the commonplane 166 defined by and containing the cable distal ends 164.Alternatively, with four beams as shown in FIG. 6a, the cable distalends 164 define and are positioned in a planar square grid 170. Thearrangements of FIGS. 6a and 6b produce a two-dimensional interferencepattern which can be observed at the recording plane 168.

In the laboratory work of the prior art, the recording plane 168coincides with the plane containing the intersecting beam centroids(i.e., the plane defined by the point of intersection of the centers ofthe three or four illuminating beams). FIGS. 6a and 6b also show theshifted illumination technique of the present invention by which thebeam centroids are displaced from (i.e., do not intersect in) therecording plane 168, but instead intersect in a shifted or offset plane172 located five to ten centimeters above and parallel to the recordingplane 168. Because the intensity of the light emerging from thefiber-optic cable distal ends 164 is greatest at the beam center anddecreases along a beam radius with a nearly gaussian distribution,angularly displacing the three (or four) illuminating beams allows for amore uniform illumination at a recording plane 168 vertically offset(e.g., by five to ten centimeters) from the beam centroid overlap plane172.

FIGS. 8a and 8b illustrate this effect for the three illumination beamembodiment of FIG. 6b. The plots of FIG. 8a and FIG. 8b represent themacroscopoic intensity distribution resulting from overlapping threeilluminating beams. On this macroscopoic scale, the intensities of thethree beams are summed and the resulting distribution is represented ina contour plot where each successively outer ring represents a drop offive per cent from the next interior or higher intensity. Also plottedin the figures is a rectangle 180 representing a two hundred fifty bytwo hundred millimeter area corresponding to a three hundred millimeterdiagonal screen area suitable for FED patterning. In the plots of FIGS.8a and 8b, the divergence of the illuminating beams is fixed. FIG. 8adepicts the illumination found in the shifted or offset plane 172 (FIG.6b) where all three beam centroids overlap. In this case the resultingintensity distribution varies with the expected gaussian profileyielding a 50% variation in the level of the illumination within therectangular target field 180. This directly impacts the feature sizerecorded in photoresist, yielding a comparable and unacceptable featuresize variation over the exposed area. One solution to this problem wouldbe to further expand the size of the illuminating beams, however thisbecomes impractical at existing laser power levels and would lead tolong exposure times and poor tool manufacturing throughput. In themethod of the present invention, the illuminating beam centroids areaxially displaced, thereby shifting the beam centroid overlap plane awayfrom the recording plane and effectively broadening the area of lowvariation illumination, the results of which are depicted in FIG. 8b,again for a fixed beam divergence. The plot of FIG. 8b represents theillumination in a recording plane 168 axially offset or shifted somedistance from the plane 172 in which the beam centroids overlap; anapparent displacement of each of the three illuminating beams isobserved. Note that a more acceptable maximum variation of only 15% inillumination level is found in the corners 182 of the rectangular targetfield 180. The optimum shift in this illumination model was eighteencentimeters measured along lines radiating out from the center to thecorners of an isosceles triangle, and the gaussian beam diameters in theplane are nearly sixty centimeters, providing ample beam overlap as isnecessary for generating the microscopic interferometric patterns.

FIG. 9 depicts the plotted experimental results (also as illuminationintensity contours over an area) for the shifted illumination techniqueof the present invention utilizing four illuminating beams, as in FIG.6a. Comparing the plots of FIG. 8b to FIG. 9, it is evident in FIG. 9that good illumination uniformity over the rectangular target 184 ismore readily obtained with four beams, yielding lower beam divergenceand smaller displacements. The illumination intensity contour curvesplotted in FIG. 9 are for a four-beam system incorporating an offset orshift of only ten centimeters with illuminating beam diameters one-thirdsmaller than those for which results are depicted in FIG. 8b. The lowerbeam divergence yields a more concentrated illumination and consequentlyshorter exposure times and higher tool manufacturing throughput.

From the foregoing description it will be appreciated that the inventionmakes available a tool and method for holographic lithography wellsuited for use in manufacturing environments, the embodiments disclosedherein are examples and many variations are possible. For example,arrays of lines suitable for grating or electrode applications may beobtained by utilizing two or three illuminating beams. Such patterns mayalso be useful in forming alignment layers for liquid crystal-baseddevices and displays. Asymmetric placement of the illuminating beams(e.g., by asymetric placement of the carriage mounted fiber positioningstages 25a, 25b, 25c on rails 136, 138 and 140) can generate a varietyof sub-micron sized structures having rectangular or oval shapes andsuitable for phase shifting optics or for patterning more arbitrarilyshaped structures for integrated circuit applications. Because themicroscopic interference patterns exist wherever the illuminating beamsoverlap, the patterning system can also be used to generate periodicstructures on arbitrarily shaped surfaces such as missile domes,aircraft canopies, and curved refractive optics.

As noted above, a variety of products could benefit from the increasedruggedness and anti-reflective performance afforded by motheye surfacingover large areas. A partial list includes applications such asautomobile or aircraft windows, protective or anti-glare screens forartwork or displays, eye or sun glasses, residential or commercialwindows, imaging systems such as cameras, telescopes, microscopes, andbinoculars, as well as photocells for use in optical sensing, opticaldata transmission and energy gathering. In addition, motheye surfacesfind application in the diamond film industry where increased surfacearea may enhance the adhesion of the diamond layers, and the surfacestructures themselves may provide a greater density of diamondnucleation sites yielding a more uniform film coating.

Having described preferred embodiments of a new and improved method andapparatus, it is believed that other modifications, variations andchanges will be suggested to those skilled in the art in view of theteachings set forth herein. It is therefore to be understood that allsuch variations, modifications and changes are believed to fall withinthe scope of the present invention as defined by the appended claims.

What is claimed is:
 1. A lithographic tool system including aninterferometric pattern generator, comprising:a coherent light sourcegenerating a coherent light source beam; means for dividing saidcoherent light source beam into first, second and third mutuallycoherent optical beams; a first optical waveguide having a first end anda second end including means for launching said first mutually coherentoptical beam into said first waveguide first end and having an opticalelement on said first waveguide second end, wherein said optical elementcauses said first mutually coherent optical beam to become a firstdivergent beam having a first centroid; a second optical waveguidehaving a first end and a second end including means for launching saidsecond mutually coherent optical beam into said second waveguide firstend and having an optical element on said second waveguide second end,wherein said optical element causes said second mutually coherentoptical beam to become a second divergent beam having a second centroid;a third optical waveguide having a first end and a second end includingmeans for launching said third mutually coherent optical beam into saidthird waveguide first end and having an optical element on said thirdwaveguide second end, wherein said optical element causes said thirdmutually coherent optical beam to become a third divergent beam having athird centroid; a platform having a substantially planar surface adaptedto support a workpiece having a selected thickness and a photosensitivesurface; a first support disposed a selected distance from the platformsurface, wherein said first support includes a first mount, and saidfirst waveguide second end is affixed to said first mount and positionedto aim said first divergent beam at said platform surface; wherein saidfirst support further includes a second mount, and said second waveguidesecond end is affixed to said second mount and positioned to aim saidsecond divergent beam at said platform surface; wherein said firstsupport further includes a third mount, and said third waveguide secondend is affixed to said third mount and positioned to aim said thirddivergent beam at said platform surface; and wherein said firstdivergent beam, said second divergent beam, and said third divergentbeam are combined to generate an interferometric pattern of light in areference plane, said reference plane being defined by overlap of saidcentroids of said first, second and third divergent beams, and saidreference plane is substantially parallel to said platform surface. 2.The lithographic tool system of claim 1, wherein said first, second andthird optical waveguides are of substantially equal length.
 3. Thelithographic tool system of claim 1, wherein said reference plane isoffset from said platform surface by an offset distance greater thansaid workpiece selected thickness.
 4. The lithographic tool system ofclaim 3, wherein said offset distance is in the range of five to tencentimeters.
 5. The lithographic tool system of claim 1, wherein saidmeans for launching said first mutually coherent optical beam into saidfirst waveguide first end comprises a collimator.
 6. The lithographictool system of claim 1, wherein said first waveguide comprises asingle-mode polarization maintaining optical fiber.
 7. The lithographictool system of claim 1, wherein said optical element on said firstwaveguide second end comprises a refractive lens.
 8. The lithographictool system of claim 1, wherein said optical element on said firstwaveguide second end comprises a diffusing optical element.
 9. Thelithographic tool system of claim 1, wherein said coherent light sourcecomprises an argon-ion gas laser.
 10. The lithographic tool system ofclaim 1, wherein said a coherent light source beam is polarized and hasa wavelength in the blue range of the visible spectrum.
 11. A method forgenerating an interferometric pattern, comprising the following methodsteps:(a) generating a coherent light source beam; (b) dividing saidcoherent light source beam into first, second and third mutuallycoherent optical beams; (c) launching said first mutually coherentoptical beam into a first waveguide first end, wherein said launchingcauses said first mutually coherent optical beam to become a firstaberrated beam having a first centroid; (d) launching said secondmutually coherent optical beam into a second waveguide first end,wherein said launching causes said second mutually coherent optical beamto become a second aberrated beam having a second centroid; (e)providing a first support at a selected distance from a substantiallyplanar platform surface, (f) placing a workpiece having a selectedthickness and a photosensitive surface on said panel surface; (g) aimingsaid first aberrated beam at said platform surface; (h) aiming saidsecond aberrated beam at said platform surface; (i) combining said firstaberrated beam and said second aberrated beam; and (j) generating aninterferometric pattern of light in a reference plane, said referenceplane being defined by overlap of said centroids of said first andsecond aberrated beams, wherein said reference plane is substantiallyparallel to said platform surface and offset from said platform surfaceby a selected offset distance greater than said workpiece selectedthickness.
 12. The method of claim 11, wherein step (b) includesdirecting said coherent light source beam toward a diffractive fanoutelement.
 13. The method of claim 11, wherein step (b) includes directingsaid coherent light source beam toward a grating coupled reflectiveoptical element.
 14. The method of claim 11, wherein step (b) includesdirecting said coherent light source beam toward a mode cross couplingintegrated optic waveguide.
 15. The method of claim 11, wherein step (b)includes directing said coherent light source beam toward a beamsplitter.
 16. The method of claim 11, wherein step (c) compriseslaunching said first mutually coherent optical beam through a diffuserat said first waveguide second end.
 17. A lithographic tool systemincluding an interferometric pattern generator, comprising:a coherentlight source generating a coherent light source beam; means for dividingsaid coherent light source beam into first, second, third and fourthmutually coherent optical beams; a first optical waveguide having afirst end and a second end including means for launching said firstmutually coherent optical beam into said first waveguide first end andhaving a diffusing optical element on said first waveguide second end,wherein said optical element causes said first mutually coherent opticalbeam to become a first divergent aberrated beam having a first centroid;a second optical waveguide having a first end and a second end includingmeans for launching said second mutually coherent optical beam into saidsecond waveguide first end and having a diffusing optical element onsaid second waveguide second end, wherein said optical element causessaid second mutually coherent optical beam to become a second divergentaberrated beam having a second centroid; a third optical waveguidehaving a first end and a second end including means for launching saidthird mutually coherent optical beam into said third waveguide first endand having a diffusing optical element on said third waveguide secondend, wherein said optical element causes said third mutually coherentoptical beam to become a third divergent aberrated beam having a thirdcentroid; a fourth optical waveguide having a first end and a second endincluding means for launching said fourth mutually coherent optical beaminto said fourth waveguide first end and having a diffusing opticalelement on said fourth waveguide second end, wherein said opticalelement causes said first mutually coherent optical beam to become afourth divergent aberrated beam having a first centroid; a platformhaving a substantially planar surface adapted to support a workpiecehaving a selected thickness and a photosensitive surface; a firstsupport disposed a selected distance from the platform surface, whereinsaid first support includes a first mount, and said first waveguidesecond end is affixed to said first mount and positioned to aim saidfirst divergent aberrated beam at said platform surface; wherein saidfirst support further includes a second mount, and said second waveguidesecond end is affixed to said second mount and positioned to aim saidsecond divergent aberrated beam at said platform surface; wherein saidfirst support further includes a third mount, and said third waveguidesecond end is affixed to said third mount and positioned to aim saidthird divergent aberrated beam at said platform surface; wherein saidfirst support further includes a fourth mount, and said fourth waveguidesecond end is affixed to said fourth mount and positioned to aim saidfourth divergent aberrated beam at said platform surface; and whereinsaid first divergent aberrated beam, said second divergent aberratedbeam, said third divergent aberrated beam and said fourth divergentaberrated beam are combined to generate an interferometric pattern oflight in a reference plane, said reference plane being defined byoverlap of said centroids of said first, second, third and fourthdivergent aberrated beams, and said reference plane is substantiallyparallel to said platform surface.
 18. The lithographic tool system ofclaim 17, wherein said first, second, third and fourth opticalwaveguides are of substantially equal length.
 19. The lithographic toolsystem of claim 17, wherein said reference plane is offset from saidplatform surface by an offset distance greater than said workpieceselected thickness.
 20. The lithographic tool system of claim 19,wherein said offset distance is in the range of five to ten centimeters.21. The lithographic tool system of claim 17, wherein said means forlaunching said first mutually coherent optical beam into said firstwaveguide first end comprises a collimator.
 22. The lithographic toolsystem of claim 17, wherein said first waveguide comprises a single-modepolarization maintaining optical fiber.